Repair announcement method and apparatus for electric injection molding machine

ABSTRACT

White noise is applied to a servocontrol system of a servomotor in order to measure a frequency characteristic of a mechanical component in an electric injection molding machine, and a signal from an encoder is applied to a fast Fourier converter. Data from the fast Fourier converter is applied to a memory unit, and the content of the memory unit is displayed on a display unit in the form of a board diagram. Repair announcement is issued when a deviation of the resonant frequency of each mechanical component with respect to data at an initial setting time exceeds a predetermined value.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromprior Japanese Patent Application No. 2005-281871, filed Sep. 28, 2005,the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and apparatus for announcementof repair of various mechanical components assembled in an electricinjection molding machine, and more particularly, to a repairannouncement method and apparatus which automatically execute diagnosticprocessing for repair announcement without applying any load on a workerin charge of operation of the electric injection molding machine.

2. Description of the Related Art

In an electric injection molding machine, which has been prevailingrecently, often uses a servomotor, for example, an AC servomotor insteadof a hydraulic drive. Generally, a rotary drive of the servomotor isapplied to a rotation direct-transmission mechanism, in which a nut anda ball screw are combined, through a pulley and a timing belt, therebyshortening the entire length of the injection molding machine to achievesaving of space for installation.

The operating condition of such an electric injection molding machinevaries depending on an individual user. For an electric injectionmolding machine of a high operation rate, the cycle of inspection needsto be short, that is, the frequency of inspection needs to be high.Under such a circumstance, it takes a lot of direct measurement time,which a worker consumes for inspection, and working time for processingdata measured for prediction of timing when a repair is needed.

Particularly, as regards inspection of timing belts, which are arrangeddispersedly, the worker needs to execute a necessary procedure such ascomparing tension measured using a tension meter and that of initialstate from values or comparing visually from graphical values, listeningto noise generated by the machine and inferring from experience, or thelike for each timing belt.

Recently, a portable sound wave type belt tension meter capable ofmeasuring the tension of a timing belt with sound waves has beenprovided to facilitate the measurement of the tension to some extent(refer to, for example, pamphlet of sound wave type belt tension U-507[5000 sheets issued by Gates Unitta Asia on Apr. 13, 2004].

The above-described conventional method, which captures change over timeof components in the drive force transmitting mechanism of theservomotor with a time passage, has not allowed the repair announcementto be executed easily. This is because a worker is always needed, only askilled person can determine such a change since there is a portiondepending on visual check or acoustic sense, it takes much time for sucha procedure, and further, there is a difference depending on anindividual person in its judging result.

As another conventional method, there is available a method of applyingvibration to a structure body of a machine with a vibration exciter anddetecting its vibration waveform at other portions with a sensor so asto analyze the characteristic of a detection portion by waveformanalysis. Such a method exaggerates the measurement work itselfincluding setting of the vibration exciter and arrangement of a sensor.Further, analysis of its cause-and-effect relationship is not easy.

Recently, a method of fast Fourier-converting a signal from an encoderby applying white noise for gain adjustment of the servosystem in anumerical control machine tool has been proposed (refer to, for example,Jpn. Pat. Appln. KOKAI Publication No. 2001-175303).

The white noise principally contains all the frequency components eachby substantially the same amount and needs to contain a frequencycomponent in a sufficient range for measurement. In the meantime, awhite noise generator used for practical purpose has been well known.

As described above, the method, which captures change over time ofcomponents in the drive force transmitting mechanism of the servomotorwith a time passage, has a problem not allowing the repair announcementto be executed easily. This is because a worker is always needed, only askilled person can determine such a change since there is a portiondepending on visual check or acoustic sense, it takes much time for sucha procedure, and further, there is a difference depending on anindividual person in its judging result.

BRIEF SUMMARY OF THE INVENTION

An object of the present invention is to provide a repair announcementmethod and repair announcement apparatus capable of announcing a repairto a mechanical component without depending on any individualmeasurement.

In order to achieve the above object, according to one aspect of thepresent invention, there is provided a repair announcement method forannouncing a repair of a mechanical component, including:

measuring a frequency response characteristic of the mechanicalcomponent at an initial installation state of the mechanical component;

determining a first frequency corresponding to a resonance point of themechanical component according to measurement data at the initialinstallation state;

measuring the frequency response characteristic of the mechanicalcomponent after a predetermined operating time elapses;

determining a second frequency corresponding to a resonance point of themechanical component according to measurement data after thepredetermined operating time elapses; and

issuing the repair announcement by judging that a timing of repairingthe mechanical component corresponding to the resonance point hasarrived when a deviation between the first frequency and the secondfrequency exceeds a predetermined allowable value.

According to the repair announcement method of the invention,measurement of a mechanical component of an electric injection moldingmachine or the like is automatically executed to judge the timing forrepair announcement. As a consequence, a worker is relieved of asubstantial measurement work. Further, content and judging result can bedisplayed on display means in the form of a board diagram and pastmeasurement data can be written over the diagram, and therefore, changesover time of the mechanical component can be compared with past data.

According to another aspect of the invention, there is provided a repairannouncing apparatus which announces repair of a mechanical component,including:

a first device which measures a frequency response characteristic of themechanical component at an initial installation state of the mechanicalcomponent;

a second device which determines a first frequency corresponding to aresonance point of the mechanical component according to the measurementdata of the first device;

a third device which measures a frequency response characteristic of themechanical component after a predetermined operating time elapses bymeans of the second device;

a fourth device which determines a second frequency corresponding to theresonance point of the mechanical component according to measurementdata of the third device; and

a fifth device which issues the repair announcement by judging that atiming of repairing the mechanical component corresponding to theresonance point has arrived when a deviation between the first frequencyand the second frequency exceeds a predetermined allowable value.

In the repair announcement apparatus of the invention, measurement datacan be obtained from a fast Fourier converting section only by applyingwhite noise to a servocontrol system of a servomotor. Thus, the workerdoes not need to prepare a detector or sensor for the measurement butcan acquire measurement data instantly at any time.

Additional advantages of the invention will be set forth in thedescription which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. Theadvantages of the invention may be realized and obtained by means of theinstrumentalities and combinations particularly pointed out hereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention, andtogether with the general description given above and the detaileddescription of the embodiments given below, serve to explain theprinciples of the invention.

FIG. 1 is a block diagram showing major portions of an apparatus formeasuring a frequency characteristic of mechanical components in anelectric injection molding machine to which the present invention isapplied;

FIG. 2A is a longitudinal sectional view taken along an injection axisdirection of an injection unit of the electric injection moldingmachine;

FIG. 2B is a longitudinal sectional view of a clamping unit of theelectric injection molding machine, the view being taken along a movingdirection of a movable die plate;

FIG. 3A is a plan view for explaining a positional relationship betweena screw advancement/retraction servomotor and a timing belt of theinjection unit of FIG. 2A;

FIG. 3B is a front view for explaining the positional relationship;

FIG. 3C is an explanatory diagram showing other means for adjusting thedegree of tension of the timing belt;

FIG. 4 is a flowchart for explaining the content of a diagnosticprogram; and

FIG. 5 is a diagram displayed on a display unit showing a board lineincluding a resonance point of each mechanical component based on singlemeasurement data.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings.

FIG. 1 is a block diagram showing major portions of a repairannouncement apparatus for measuring a frequency characteristic of amechanical component in an electric injection molding machine accordingto the present invention. In the figure, reference numeral 10 denotes aposition instructing section which constitutes part of a control unit ofthe electric injection molding machine. Reference numeral 12 denotes aservocontrol system (control block) which applies a drive instructioncurrent to the servomotor 14. An output shaft 18 of a servomotor 14 isprovided with a rotary encoder 20. An end of a timing belt 16 isattached to the output shaft 18 through a pulley (not shown), and theother end of the timing belt 16 is attached to a ball screw shaft 44 ofan injection unit 30 described later which substantially serves as aload of the servomotor 14.

The servocontrol system 12 includes an adder AD1, a position controlsection 31, a velocity control section 32, a current control section 33,a differential circuit 34 which generates a velocity feedback signal bycalculating a difference of outputs (pulse string) from the encoder 20and applies the signal to the adder AD2, and an integration circuit 35which generates a position feedback signal by integrating the velocityfeedback signal and applies the signal to the adder AD1.

Reference numeral 100 denotes a white noise generator for generatingwhite noise WNZ. The white noise WNZ is a so-called white noise signalwhich contains substantially all the frequency components for actualpurpose. Reference numeral 22 denotes a fast Fourier converting section.An output of the differential circuit 34 is input to the convertingsection 22, and the white noise WNZ from the white noise generator 100is also input thereto.

Contact points C1, C2 for setting the servocontrol system 12 to ameasurement mode can be changed over by a mode change instruction MODfrom a control unit 28, and the white noise WNZ is given to the velocitycontrol section 32 according to the change instruction MOD thereby toseparate the position control section 31 from the velocity controlsection 32.

Reference numeral 26 denotes a memory unit, which includes a firstmemory area MA1 and a second memory area MA2. The first memory area MA1directly stores output data from the fast Fourier converting section 22.The second memory area MA2 stores data of the first memory area MA1, aresonance point peak value P(i) of each mechanical component based onthe data, a resonant frequency F(i) of the peak value, a deviation valueS(i) of the resonant frequency F(i) with respect to the data at initialsetting time, and a judging result of whether or not the deviation valueS(i) exceeds an allowable range Δf(i) set preliminarily in a thirdmemory area MA3. The memory unit 26 further includes a memory area 26Afor storing programs PG1, PG2 and PG3.

The program PG1 is a diagnostic program. The program PG2 is a programfor calculating data such as the peak value, resonant frequency,deviation value, judging result calculated based on the data in thefirst memory area MA1 and for storing the data stored in the firstmemory area MA1 and the data obtained by the calculation in the secondmemory area MA2. The program PG3 is a program for displaying data storedin the first memory area MA1 or data stored in the second memory areaMA2 on a screen of a display unit 24 in the form of a board diagram.These programs PG2 and PG3 constitute a subroutine of the program PG1.The contents of the respective PG1 to PG3 are read and executed by a CPU27 serving as a processing unit included in the memory unit 26. In themeantime, the CPU 27, the programs PG1, PG2 and PG3, and the thirdmemory area MA3 may be provided in another control unit 28 instead ofthe memory unit 26. The white noise generator 100 and the fast Fourierconverting section 22 are incorporated as components constituting thecontrol unit 28.

FIGS. 2A and 2B show major portions of the injection unit 30 and aclamper unit 36 for use in the electric injection molding machine. FIG.2A is a longitudinal sectional view of the injection unit 30 taken alongthe injection axis direction, and FIG. 2B is a longitudinal sectionalview of the clamper unit 36 taken along the moving direction of amovable die plate 56.

In FIG. 2A, reference numeral 40 denotes a barrel, 42 denotes a hopper,46 denotes a screw for injection, and 44 denotes a ball screw shaft. Arotation of the servomotor 14 for screw advancement and retraction istransmitted as a rotation of a ball nut 45 through the timing belt 16 soas to advance or retract the ball screw shaft 44 in the axial direction.A base 44A can advance or retract in the axial direction integrally withthe ball screw shaft 44 and is connected to a pulley section 46A througha bearing section 44B such that no rotation is transmitted. Thus, arotation of the servomotor 14B for screw rotation is given from thepulley to the screw 46 through the timing belt 16B.

The damper 36 of FIG. 2B is provided with the movable die plate 56 whichopposes a fixed die plate 58 at the right end of the figure andadvances/retracts along a tie-bar 57, and the left side of the movabledie plate 56 on the figure is coupled with a toggle link 52. An upperside of FIG. 2B shows the toggle link 52 in a state of substantiallystretched, while a lower side thereof shows the toggle link 52 in astate of being substantially contracted. A cross head 50 is coupled withan intermediate link of the toggle link 52, and the head fixed with anut is screwed together with a ball screw shaft 50A. The ball screwshaft 50A is driven by a die clamping servomotor 14C through the pulleyand timing belt 16C. Thus, the cross head 50 is advanced or retracted inthe axial direction by a rotation of the servomotor 14C, so that thetoggle link 52 is stretched or contracted as shown in the figure so asto advance or retract the movable die plate 56 with respect to the fixeddie plate 58. In the meantime, the left end of the toggle link 52 isattached to a link housing 53. The position of the link housing 53 inthe axial direction is adjusted depending on the thickness of the die(die height). In the meantime, reference numeral 14D denotes a componentfor advancing or retracting a push plate 54 for pushing out a moldedarticle and advances or retracts the ball screw shaft 54B integral withthe plate 54 through the timing belt 54A and a nut.

FIGS. 3A to 3C are diagrams for explaining a positional relation betweenthe servomotor 14 for screw advancement/retraction of the injection unit30 and the timing belt 16 in FIG. 2A. FIG. 3A is a plan view, FIG. 3B isa front view, and FIG. 3C shows other means for adjusting the tension ofthe belt. FIGS. 2A and 2B indicate that the output shaft of theservomotor 14 fixed to a mounting member 62 on a fixing base 64 can bedisplaced in the right and left direction in the figure by an adjustmentscrew 60, which makes it possible to adjust the tension of the timingbelt 16 applied to the outer periphery of the pulleys PL1 and PL2.

In FIG. 3C, the tension of the timing belt is adjusted by adjusting atension adjusting section ADJ, having another pulley PL3 halfway of thebelt, vertically from a base FPL provided on the fixing position sidewith a screw instead of shifting the position of the servomotor 14 asindicated in FIGS. 3A and 3B.

The above-described electric injection molding machine includes the samenumber of drive power transmitting mechanisms as that of installedservomotors, and periodic inspection and maintenance are indispensableto maintain an appropriate operating condition. In the periodicinspection and maintenance, inspection locations, inspection content andinspection cycle are different depending on each inspection andmaintenance, and for example, the inspection content and inspectioncycle are not the same between the timing belt and a coupling section ofthe ball screw shaft and nut. That is, change over time of fatigue ofthe timing belt for receiving a stress repeatedly at operation time interms of a material and change over time of abrasion at the couplingsection are quite different in terms of the degree of progress, so thatthe timing belt has a higher inspection frequency. For this reason,other components such as the coupling section may not be inspected atthe time of inspection of the timing belt.

On the other hand, a manufacturer provides a system, which allowsinspected portions of the electric injection molding machine installedon the user side to be repaired when the machine is still in anappropriate operating condition, on the basis of a result of periodicinspection in order to prevent the machine from suddenly failing due toa fault or the like.

Consideration has been made with respect to the above-described problemsabout announcement of repair on mechanical components such as the timingbelt, ball screw shaft and nut which constitute the mechanicalcomponents of the electric injection molding machine, particularly, thetransmitting mechanism for transmitting a drive force of the servomotor.As a result, the present invention is developed considering and using afact that a frequency of a resonance point corresponding to eachmechanical component is shifted corresponding to a change over time ofeach component by processing data obtained by fast Fourier converting asignal from the encoder with white noise applied to the servocontrolsystem of the servomotor.

Next, the operation contents of the programs PG1, PG2 and PG3 by the CPU27 with the above-described configuration will be described withreference to a flowchart of FIG. 4.

Referring to FIG. 4, the mode change instruction MOD is output from thecontrol unit 28 to the contact points C1 and C2 in step ST1, so that theservocontrol system 12 is changed over to a measurement mode and thewhite noise WNZ is given from the white noise generator 100.

Next, in step ST2, output data from the fast Fourier converting section22 is stored in the first memory area MA1. Further, data of the firstmemory area MA1 and respective data about a resonance point peak valueP(i) of each mechanical component, a resonant frequency F(i) of the peakvalue and a deviation value S(i) of the resonant frequency F(i) withrespect to the data at initial setting time, generated based on the dataof the first memory area MA1, are stored in the second memory area MA2.Those are displayed on the screen of the display unit 24. In this case,those data may be displayed together with measurement data at theinitial setting time.

Next, in step ST3, an index i of each mechanical component, which is anobject of measurement, is set to 1.

Then, in steps ST4 and ST5, the resonant frequencies F0(Pi) and F(Pi) ofeach mechanical component i obtained by measurement at the initialsetting time and after operation for a predetermined period are read. Instep ST6, a deviation S(i) is obtained and in step ST7, it is determinedwhether or not the deviation value (absolute value) is within itsallowable range. The determination result is stored in the second memoryarea MA2. Then, if the allowable range is exceeded, the determinationcontent is stored in the second memory area MA2 in step ST9, and anannouncement for repair, that is, an alarm is displayed on the displayunit 24.

If the result is within the allowable range in step ST7, thedetermination result is stored in the second memory area MA2, and amessage, indicating there is leeway until the announcement of repair, isdisplayed on the display unit 24.

Next, in step ST10, it is determined whether or not an index i of acertain mechanical component, which is an object for measurement,reaches a number N. If i=N, the procedure ends, and otherwise, i=i+1 isperformed in step ST1, and the procedure proceeds to step ST4.

FIG. 5 shows the resonance points P1, P2 and P3 of each mechanicalcomponent based on single measurement data displayed on the boarddiagram. This example is a case where the aforementioned N is 3, inwhich i=1 corresponds to the timing belt, i=2 corresponds to the ballscrew shaft, and i=3 corresponds to other components, which aremechanical components. According to an actual measurement, it isobserved that the resonance point of each mechanical component isusually shifted to the left due to the operation while time elapses. Theshift amount differs depending on each component. Each shift amountenables the repair announcement of each mechanical component. That is,when a deviation value with respect to the data at initial setting timeof the resonant frequency of each mechanical component exceeds apredetermined value, the repair announcement is issued.

According to the embodiment of the invention, as described above, therepair announcement is enabled to announce a repair to a mechanicalcomponent without depending on any individual measurement.

Although the embodiments of the invention have been described above, thepresent invention is not restricted to these exemplified embodiments butmay be modified in various ways. For example, it is permissible to applythe white noise WNZ to the servocontrol system at the same time when aposition instruction is applied without changing modes.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A repair announcement method for announcing a repair of a mechanicalcomponent, comprising: measuring a frequency response characteristic ofthe mechanical component at an initial installation state of themechanical component; determining a first frequency corresponding to aresonance point of the mechanical component according to measurementdata at the initial installation state; measuring the frequency responsecharacteristic of the mechanical component after a predeterminedoperating time elapses; determining a second frequency corresponding toa resonance point of the mechanical component according to measurementdata after the predetermined operating time elapses; and issuing therepair announcement by judging that a timing of repairing the mechanicalcomponent corresponding to the resonance point has arrived when adeviation between the first frequency and the second frequency exceeds apredetermined allowable value.
 2. The repair announcement methodaccording to claim 1, wherein said each measuring is executed byapplying white noise to a servocontrol system of a servomotor serving asthe mechanical component.
 3. The repair announcement method according toclaim 1, wherein in said each measuring, each measurement data is storedon a memory, and the stored data is read from the memory and displayedtogether on a board diagram on a screen of display means.
 4. The repairannouncement method according to claim 3, wherein the third step isexecuted plural times, so that data of plural measurement are writtentogether on the board diagram on the screen of the display means so asto display a change over time.
 5. A repair announcing apparatus whichannounces repair of a mechanical component, comprising: a first devicewhich measures a frequency response characteristic of the mechanicalcomponent at an initial installation state of the mechanical component;a second device which determines a first frequency corresponding to aresonance point of the mechanical component according to the measurementdata of the first device; a third device which measures a frequencyresponse characteristic of the mechanical component after apredetermined operating time elapses by means of the second device; afourth device which determines a second frequency corresponding to theresonance point of the mechanical component according to measurementdata of the third device; and a fifth device which issues the repairannouncement by judging that a timing of repairing the mechanicalcomponent corresponding to the resonance point arrives when a deviationbetween the first frequency and the second frequency exceeds apredetermined allowable value.
 6. A repair announcing apparatusaccording to claim 5, wherein the first device includes: a servomotorarranged in an electric injection molding machine; a servocontrol systemfor the servomotor; a white noise generator which generates white noiseto be applied to the servocontrol system; an encoder which feeds back arotation of the servomotor; a fast Fourier converter which receives adifference between white noise from the white noise generator and anoutput of the encoder and applies fast Fourier conversion to thedifference; a memory unit which stores output data from the fast Fourierconverter; and a display device which displays contents of the memorydevice.
 7. The repair announcing apparatus according to claim 6, whereinthe memory unit includes: a first memory area which stores output datafrom the fast Fourier converter; and a second memory area which storesdata of the first memory area, a resonant frequency of a peak valuecorresponding to said each mechanical component calculated based on thedata, and a deviation value of the resonant frequency with respect tothe data at initial setting time.
 8. The repair announcing apparatusaccording to claim 7, wherein the memory unit further includes a programwhich converts data of the first memory area to the second memory areaand stores the converted data.
 9. The repair announcing apparatusaccording to claim 8, wherein the memory unit further includes a programwhich displays data of the second memory on the screen of the displaydevice in the form of a board diagram.
 10. The repair announcingapparatus according to claim 6, further comprising a servocontrol systemmode changing device which changes the servocontrol system to ameasurement mode in order to activate the first device effectively.